In production apparatuses and production lines of semiconductor devices, FPD glass substrates, and other electronic components, for example, the electronic components or substrates thereof are irradiated with soft X-rays having a wavelength of 1 Å to several hundred Å for removing static electricity therefrom, the soft X-rays being X-rays of a long-wavelength range (low energy range).
Regarding an X-ray generation method itself, static elimination apparatuses for irradiating soft X-rays for static elimination as described above basically use the same means as in the prior art.
Specifically, a typical generation method involves heating a filament as an electron emission source to several hundred ° C. or more in a vacuum atmosphere and applying a negative voltage to a circumference of the filament so that electrons are emitted. Due to the electron emission at a high temperature, the emitted electrons are generally called thermal electrons. The emitted thermal electrons are accelerated toward a positive potential side by an electric field and eventually collide with a vacuum tube constituent member (so-called target). Because an energy of the electrons is determined based on a difference of application voltage, when a potential of the filament as the electron emitting portion is −9 kV and a potential of the member with which the electrons collide is 0 V, for example, a kinetic energy of the emitted electrons is 9 keV.
X-rays are generated by using a material that is apt to emit braking X-rays or characteristic X-rays for the target with which the electrons emitted from the electron emitting portion collide. Generally, as the material for the X-ray target of this type, W, Ti, Cu, Mo, and the like are mainly used. Regarding a thickness of the target, though an optimal thickness is specified based on, in a case of a transmission type, a relationship between an electron ingression depth and a soft X-ray transmittance, a thickness of about 0.1 μm to 10 μm is generally used. On the other hand, in a case of a reflection type, the thickness only needs to be equal to or more than the electron ingression depth, and the X-rays generated from the target member whose thickness is not particularly limited are transmitted through a window constituted of a member that transmits X-rays relatively easily to thus be emitted to the outside.
For increasing an X-ray amount in an X-ray generation apparatus based on the generation principle as described above, it is necessary to increase an amount of electrons to be generated. For example, for increasing the X-ray amount by tenfold, the amount of electrons to be generated also needs to be increased by tenfold. In this case, for increasing the number of electrons by 10 folds without changing an applied voltage, it is necessary to either increase an electron generation surface area of the filament or additionally raise the filament temperature, but in either case, calorific value is largely increased. A large proportion of heat generation of the X-ray generation apparatus of the prior art occurs in such an electron generation portion, and heat generation caused by an electron current (=electron current×voltage) is no more than about 10 to 25% of the entire heat generation.
Reviewing the prior art while taking the above descriptions into consideration, an X-ray generation apparatus used in Patent Document 1 (Japanese Patent No. 2749202) uses a target member in which a thin target film formed of a material that emits X-rays after receiving electrons is formed on an X-ray transmissive substrate, the X-ray generation apparatus provided with a grid electrode between a filament and the target.
In Patent Document 2 (Japanese Patent Application Laid-open No. 2005-11635), a negative voltage with respect to a target is applied to a filament after the filament is energized and heated to several hundred ° C. or more, whereby thermal electrons are irradiated onto the target.
Similarly in Patent Document 3 (Japanese Patent Application Laid-open No. 2001-266780), thermal electrons are used as electrons with respect to an X-ray target.
Similarly in Patent Document 4 (Japanese Patent Application Laid-open No. Hei 7-211273), thermal electrons generated from a bar-type filament are used as electrons with respect to an X-ray target.
[Patent Document 1] Japanese Patent No. 2749202
[Patent Document 2] Japanese Patent Application Laid-open No. 2005-116354
[Patent Document 3] Japanese Patent Application Laid-open No. 2001-266780
[Patent Document 4] Japanese Patent Application Laid-open No. Hei 7-211273